Barrett's esophagus (BE), a sequela of chronic gastroesophageal reflux disease (GERD), is a premalignant condition that increases an individual's chance of developing esophageal adenocarcinoma (EAC) by 30-125- fold. The precise prevalence of BE among patients with GERD is unknown but has been estimated at 1-10% of the general population (2). EAC is one of the most rapidly increasing cancers in the United States. Therefore, subjects with BE are enrolled in surveillance programs in which they undergo endoscopy at regular intervals for the rest of their lives. Due to frequent endoscopic surveillance, BE has become, by default, a de facto human model of early human preneoplastic events. Unlike colorectal adenomas, the premalignant lesions at the other end of the GI tract, the at-risk organ is left in place for repeat serial observations, often for 30 or 40 years. This BE model lends itself quite readily to molecular genetic studies in which tissue is the issue. In human diseased tissue-based studies, there is no problem with clinical relevance, and one doesn't need to worry about being led down the (proverbial) garden path by the sometimes irrelevant findings (traps) that often crop up in nonhuman or in vitro models of human disease. Methylation has been reported in many human malignancies and premalignant syndromes, but was first reported in BE and EAC 11 years ago. Tumor suppressor genes affected by hypermethylation at various stages of BN include p16, p14, E-cadherin, APC, and others. However, these reports have all been candidate gene studies, based on the usual suspects, typically focusing on the tumor suppressor gene of the month. Our Preliminary Data suggest that an unbiased, epigenome-wide approach to this aspect of BN molecular genetics is likely to shift the paradigm in several ways: 1) the predominant epigenomic change in progression appears to be hypomethylation, rather than hypermethylation, implying the activation or unmasking of growth-stimulatory genes; 2) some genes change their methylation levels late during the run-up to progression, while others change earlier; this finding implies that by using arrays, we can a) for the future, find better early predictive biomarkers of progression; b) for the current project, dissect out the temporal epigenomic program of Barrett's neoplastic development. Hypothesis: The global methylation profile of Barrett's esophagus is in a constant state of flux and changes continuously as Barrett's evolves from early pre-progression, to later pre-progression, to LGD, to HGD, and finally to EAC. Changes that occur in this profile reflect changes in biology that cause or result from this process of preneoplastic and neoplastic evolution. By comprehensively harvesting genes that are epigenetically altered at different timepoints prior to and during progression, then feeding them into gene ontology programs and databases, we will gain novel insights into the cellular and biochemical pathways that become activated (or, in the case of hypermethylation, inactivated) as Barrett's pre-progression and its later neoplastic stages proceed.